Document advanced kubernetes scheduler and security features

[NissesSenap]

Got a question today about securityContext in our cluster.
We need to document how we use OPA gatekeeper and what it applies.
Help the tenants that is ready for it to apply it to there own yaml to make it less magic and hopefully apply even harder restrictions where they can.

We need to give some best practices around PDB and talk about the need to have replicas>2 if you use it.

Talk about anti affinity and a few basic recommendations around it.

Also talk about taints and how that can be used on there pods if they have those use cases but also point out that they will need us to setup custom node pool if they want to do something like GPU based nodes together with taints.